Lloyd Girton Humphreys (December 12, 1913 – September 7, 2003) was an American differential psychologist and methodologist who focused on assessing individual differences in human behavior. His work is among the most widely cited in intelligence research, and he received many prestigious awards in this field. Born in Lorane, Oregon, Humphreys earned his undergraduate degree at the University of Oregon in 1935, a master's from Indiana University in 1936, where he first learned about factor analysis, then received his doctorate at Stanford in 1938, studying under Ernest Hilgard. His dissertation on the (or the Humphreys effect), is considered a classic in the field.